The present invention relates to a method of preventing inconsistency between data maintained in a master exchange and in its backup exchange in a telecommunication system. The invention also relates to a telecommunication system comprising a master exchange including memory means for storing data and means for updating the stored data in response to data received from other parts of the system, a backup exchange having a data transmission connection with the master exchange, the backup exchange including means for receiving and storing in a memory means the data stored in the memory means of the master exchange for keeping a back-up copy of the data stored in the memory means of the master exchange.
The present invention relates particularly to maintaining data in exchanges of mobile communication systems, although the invention can also be utilized in other connections. The invention can be utilized in a telecommunication system where a backup exchange is designated for a master exchange to ensure the operation of the system, the backup exchange keeping a back-up copy of the data stored in a master exchange database. In some systems, the backup exchange can, if required, replace the master exchange by undertaking its tasks, whereby the operation of the entire system is not interrupted even if the master exchange is, for some reason, prevented from operation.
The problem in such a communication system described above is that if a data transmission connection is for some reason cut off, updatings performed in different parts of the system are not necessarily transmitted to both exchanges, whereby databases in the master exchange and in the backup exchange can include deviant information (for example relating to a particular subscriber), i.e. their data is mutually inconsistent.
The aim of the present invention is to solve the problem described above and provide a method of preventing data inconsistency between the master exchange and its backup exchange in a telecommunication system. This object is achieved by the method of the invention characterized by keeping a copy of the master exchange data in a slave exchange having a data transmission connection with the master exchange and the backup exchange, and when the slave exchange receives data from the master exchange or from the backup exchange: the received data or the corresponding data previously stored in the slave register is selected -for use on the basis of a comparison of information included in the update information of said data, the data stored in the slave exchange is sent to the exchange that has sent the received data if the data stored in the slave exchange is selected for use, the received data is sent to the master exchange if the data received from the backup exchange is selected for use, and the received data is stored in the slave exchange if the received data is selected for use.
The invention is based on the idea that when a copy of the master exchange data is kept in the backup exchange and also in the slave exchange having a data transmission connection with the master exchange and the backup exchange, the slave exchange can then detect a potential inconsistency between the master exchange and the backup exchange data on the basis of the update information in the data received by the slave exchange, and start eliminating the inconsistency. The method of the invention enables the prevention of the inconsistency in situations where disturbances occur in a telecommunication system. This improves the reliability of the system dramatically.
In a preferred embodiment of the invention, the decision on the data the slave exchange selects for use is based on an age stamp included in the update information of the data. The slave exchange selects for use the data which has last been updated. Thus, updatings performed to the data during disturbance can also be taken into account, and situations do not occur where an updating is lost because of a system disturbance.
In another preferred embodiment of the invention, the decision on the data the slave exchange selects for use depends on who has last updated data on the basis of the update information. Thus, it can be defined for example that the data updated by the operator is selected for use rather than the data updated by the subscriber himself.
The invention also relates to a telecommunication system wherein the method of the invention can be applied. The system of the invention is characterized in that the system comprises at least one slave exchange having a data transmission connection with the master exchange and the backup exchange, the slave exchange comprising: communication means for receiving data from the master exchange and the backup exchange, comparison means for selecting for use either the received data or corresponding data stored in a memory means of the slave exchange on the basis of the update information of said data, and processing means arranged:
to send the data stored in the memory means of the slave exchange to the exchange having sent the received data when the comparison means have selected for use the data stored in the memory means of the slave exchange,
to store the received data in the memory means of the slave exchange when the comparison means have selected for use the received data, and
to send the received data to the master exchange when the comparison means have selected for use the data received from the backup exchange.
The preferred embodiments of the method and telecommunication system are disclosed in the attached dependent claims 2 to 3 and 5 to 7.